We're all "guessing" or rather, speculating. The driver changes are just circumstantial evidence that JBL was trying to improve a product that had problems.
As for the AlNiCo change to ferrite being an issue, I'm sure it was. But has anyone found a ferrite driver in a JBL that was actually inferior to the previously used AlNiCo? I've never heard that complaint. The romantic view of the AlNiCo drivers and the blue frames and motors seems to be just that—blinded by the romance of vintage. Now those "new' ferrite drivers are vintage.
I view the A/H (magnet) driver preference they way I do tube/SS and dark chocolate / milk chocolate. Everyone likes what they like and like religion, ... I have no interest in proselytizing any particular technology.
When I was young, tubes were phasing out for the new technology, AlNiCo followed 20 years later, and we were all buying the new stuff not debating whether we knew more than companies like JBL, McIntosh
et al. I do know that digital never has replaced analog in some people's homes (although in the sources and processing of the music it has), but most every other change eventually has been accepted as it hit the market as an improvement.
I consider myself very fortunate to have been on this stereo ride for over half a century, having experienced so many evolutionary and revolutionary changes, having the facilities to hear the difference (most of the time), and the budget (again most of the time) to own the systems that make me happy.
In my collecting/vintage phase I went through un-boxing many of my old systems and components, buying many more, meticulously servicing each, comparing the sound, and I have no doubt that there are many different sounds that we heard back then. Objectively the newer is always more accurate, more powerful, more "flat", linear, cleaner, quieter, ... all of the adjectives that would equate to the sound-pressure waves following the signal more closely and that is my preference. My wife OTOH really likes the sound of a 1960s era Mc tube amplifier, so that to me means that more accurate / modern still doesn't mean the most pleasant for everyone. My choice of super-accurate monitors room-corrected and EQ'ed to be as flat and perfect in-room as can be works for my obsessive by-the-numbers Engineer side and sounds great to me, where my wife prefers a bit of boost in the LF and tapering back the HF so it softens the sound a bit.
I have A/Bed so many speakers and components solo, with my wife, with my Musician son, with my Sound Engineer BIL, trying to detect "better" and most of the time it's between two very musical choices that need to be swapped multiple times to identify a difference if at all. Back in the 1970s, we did the same with multiple pairs of speakers from multiple manufacturers, and there definately was a difference. I do recall (for example) comparing the (new) L166 to the L100, hearing HF detail that was so much more abundant, and LF that had more authority. Of course my choice became clear. I never (in my recollection) however had a stereo shop line up an AlNiCo vs ferrite magnet model to compare. I can't recall anybody at the time pointing to the new model and saying that it didn't sound as good because of the new magnet.
So if anyone cares what my opinion is on the matter of L65 Jubals or Klipsch Heresey or (name your vintage) speaker is whatever makes you smile, looks good to you, brings back the best memories, makes your toes start tapping with your favorite music, can bring tears to your eyes is the best and nobody should tell you otherwise. I have my opinion on the magnet evolution (my present system's magnets are neodymium and I never questioned whether it is better) and it's just my taste.
And BTW, dark chocolate is better.
